Abstract: Aedes mosquitoes continue to transmit viruses such as dengue, Zika and yellow fever, with much of the world?s population at risk. This is particularly true in Brazil, where dengue epidemics are continuous, where the Zika epidemic hit hardest, and where urban yellow fever continually threatens to re-emerge. In order to establish new vector control strategies, Brazil has pioneered the testing and approval of a new strategy called Release of Insects with Dominant Lethality (RIDL), based on the intellectual property of Oxitec, LLC. RIDL relies on the mass release of male Ae. aegypti mosquitoes; mating with wild females results in progeny that die as late larvae or pupae. While field trials have demonstrated successful population suppression, obstacles to the widespread use of the technology include difficulty in monitoring, competitiveness of released males, cost of antibiotic used to suppress the lethal phenotype at factory scale, and rapid recovery of the mosquito population once releases cease. Modeling suggests that the release of pathogen-resistant mosquitoes following a population suppression campaign can result in the establishment of the resistance phenotype, a so called ?reduce and replace? approach that could more permanently block transmission. To develop a reduce and replace system for the control of dengue/Zika transmission, a transgenic conditional sterility system in Ae. aegypti will be established (Aim 1). Unlike current approaches where factory-scale rearing of released males must occur in the presence of tetracycline, such an approach necessitates antibiotic use only in the egg production colony, substantially reducing costs. Early embryonic lethality will in turn simplify monitoring approaches. This project will also develop a death-upon-infection strain of Ae. aegypti that will provide broad resistance across all mosquito-borne flaviviruses (Aim 2). This innovative approach takes advantage of progress already made in navigating transgenic Ae. aegypti through the regulatory process in Brazil, and the products to be developed are anticipated to directly enter the risk assessment process for field-based testing at the conclusion of this work.